Currently Being ModeratedMar 18, 2012 1:30 PM (in response to dsch)
For what it's worth....
I have a Laserwriter 16/600, very similar to your 12/640. I have an Airport Express in my den with ethernet cable running from there to the printer and I can print wireless from anywhere in range.
You have to set your APX to join a wireless network (using WDS).